wget ftp://ftp.univie.ac.at/systems/linux/dag/redhat/el5/en/x86_64/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
rpm -Uvh
rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

yum install mercurial